This invention relates to the use of electromagnetic wave energy to alter a substrate, e.g., by heat, ablation, and/or photochemical reaction.
Lasers are useful in medical, materials processing, and other applications to cause heating and/or ablation, i.e., substance removal, within a substrate, e.g., biological tissue or other material. In addition, certain lasers, e.g., ultraviolet (UV) lasers, can be used to cause photochemical alterations, e.g., polymerization, in a substrate, with or without simultaneous ablation.
Laser energy is typically delivered as a beam or illumination in which the electromagnetic energy propagates directly into the tissue or other substrate. Ablation of biological tissue by lasers occurs predominantly by the rapid thermal vaporization of tissue water. However, secondary processes may coexist with this thermal vaporization. For example, explosive mechanical removal is caused by short laser pulses when laser energy intensity is high enough to initiate a plasma that produces shock waves and mechanical fracture, e.g., greater than about 108 W/cm2. Additionally, UV pulsed laser ablation can cause concurrent photochemical reactions in tissue. When present, these secondary processes can change the efficiency of pulsed laser ablation.
The ablation depth within tissue or other materials depends upon the depth to which the electromagnetic waves penetrate. For some applications, e.g., treatment of large tumors, deep or subsurface penetration is required, and appropriate wavelength regions, e.g., red or near infrared, are preferable. For other applications, a well-controlled superficial effect is desired, e.g., skin resurfacing, ablation of the outer surface of the cornea to correct vision, or of the inner surface of diseased arteries. Typically, laser energy is delivered to a patient at normal incidence, and the wavelength of the laser energy is selected to produce the desired penetration depth based on the optical absorption of the target tissue and any intermediate tissue.
The invention features systems and tools for controlling the optical penetration depth of laser energy, e.g., when delivering laser energy to target tissue in a patient. The systems and tools control the optical penetration depth (OPD) by controlling the incident angle at which the laser energy is delivered to the target area of the patient. Embodiments of the invention include an optical coupler that permit a user to vary the incident angle and thereby selectably control the OPD of incident laser energy. Fabricating the optical coupler to have a refractive index greater than that of the target tissue can enhance the range of selectable OPDs. The laser energy, which is delivered to the desired depth, can cause alteration of the target tissue by, e.g., heating, ablation, and/or photochemical reaction.
In general, in one aspect, the invention features an apparatus delivering laser radiation to a substrate at a controlled penetration depth, the substrate having a first refractive index and an absorption coefficient xcexca. The apparatus includes an optical coupler for receiving optical energy from a optical energy source and a positioning mechanism. The optical coupler has a second refractive index higher than the first refractive index and is adapted to contact and form an interface with the substrate. It also has a contoured surface such that an angle of refraction xcex8r of the optical energy into the substrate at the interface can be varied by adjusting relative positions of the optical coupler and the optical energy entering the optical coupler. Selection of a particular angle of refraction produces a desired penetration depth xcex4r according to the equation xcex43≈(1/xcexca)cos xcex8r. The positioning mechanism couples the optical coupler and the optical energy to adjust the relative positions of the optical coupler and the optical energy entering the optical coupler.
The optical coupler may have, e.g., a hemispherical shape or a hemicylindrical shape. The positioning mechanism can be angular positioning mechanism, for example, it can include a gimbal mounted to the optical coupler. Alternatively, the positioning mechanism can be a translational positioning mechanism, e.g., it can include a support structure slidably connected to the optical coupler. Furthermore, the optical coupler can be configured to receive the optical energy at substantially normal incidence and deliver the optical energy to the interface at non-normal incidence.
In general, in another aspect, the invention features, another apparatus delivering laser radiation to a substrate at a controlled penetration depth, the substrate having a first refractive index n1 and an absorption coefficient xcexca. The second apparatus includes an optical coupler for receiving optical energy from a optical energy source. The optical coupler has a second refractive index n2 higher than the first refractive index. The optical coupler also has at least two surfaces adapted to contact and form an interface with the substrate. It is shaped to internally direct the optical energy received from the optical energy source to the first surface at a first acute incident angle, and direct optical energy internally reflected from the first surface to the second surface at a second acute incident angle different from the first acute incident angle. Contacting the substrate with the first surface produces an optical penetration depth xcex4r1≈(1/xcexca)cos xcex8r1, whereas contacting the substrate with the second surface produces an optical penetration depth xcex4r2≈(1/xcexca)cos xcex8r2, where xcex8r1 is the refraction angle corresponding to the first acute incident angle and xcex8r2 is the refraction angle corresponding to the second acute incident angle.
The optical coupler may further include a third surface adapted to contact and form an interface with the substrate. In this case, the optical coupler is shaped to direct the optical energy internally reflected from the second surface to the third surface at a third acute incident angle. In some embodiments, the first and second acute incident angles can both greater than arcsin(n0/n2), n0 being the refractive index for air, and/or they can both be less than arcsin(n1/n2). Furthermore, the first and second acute incident angles can be each greater than about 10xc2x0.
In general, in another aspect, the invention features another apparatus delivering laser radiation to a substrate at a controlled penetration depth, the substrate having a first refractive index n1 and an absorption coefficient xcexca. The third apparatus includes: an optical coupler base; and a plurality of optical coupler tips each configured to be mechanically attached to the optical coupler base to form an optical coupler for delivering optical energy from a optical energy source to a substrate. The optical coupler includes a surface adapted to contact and form an interface with the substrate. Each optical coupler tip, when attached to the optical coupler base, is shaped to internally deliver the optical energy to the interface at an incident angle, wherein the incident angles corresponding to each of the plurality of optical coupler tips differ from one another. Selecting one of the optical coupler tips specifies a desired penetration depth xcex4r, according to the equation xcex4r≈(1/xcexca)cos xcex8r, where xcex8r is the refraction angle corresponding to the incident angle defined by the selected optical coupler tip.
In some embodiments, each of the optical coupler tips has a refractive index greater than the first refractive index n1. Moreover, the plurality of optical coupler tips may include at least three optical coupler tips. The incident angle defined by each optical coupler tip may be greater than about 10xc2x0. Furthermore, the incident angle defined by each optical coupler tip may be greater than arcsin(n0/n2), where n0 is the refractive index for air and n2 is the refractive index of the respective optical coupler tip. Also, the incident angle defined by each optical coupler tip may be less than arcsin(n1/n2), where n2 is the refractive index of the respective optical coupler tip.
Embodiments of any of the first, second, and third apparatus described above may include any of the following features.
The apparatus may include an optical fiber mechanically coupled to the optical coupler or optical coupler base. The optical coupler or each of optical coupler tips may be made from one of sapphire, fused silica, BK-7 glass, flint glass, germanium, and zinc selenide. The apparatus may further including the optical energy source. The optical energy source may includes a Nd:YAG laser, CTE:YAG laser, ErCr:YSGG laser, holmium laser, erbium laser, CO2 laser, diode laser, or dye laser. For example, suitable wavelength ranges include 1.7 to 2.2 xcexcm, 2.7 to 3.2 xcexcm, 10.6 xcexcm, and 420 to 510 nm.
In general, in another aspect, the invention features a method of removing wrinkles in a region of skin. The method includes: applying an optical coupler to the region to cause a surface of the optical coupler to contact the ridges of the wrinkles and be spaced from the valleys of the wrinkles; and delivering optical energy from a optical energy source through the optical coupler to the surface at an incident angle that is greater than about arcsin(n0/n2) and less than about arcsin(n1/n2), where n0, n1, and n2 are the refractive indices of air, the skin, and the optical coupler, respectively. The optical energy is delivered with energy sufficient to smooth over the ridges of the wrinkles.
Embodiments of the method may include any of the following features.
The optical energy may be delivered to the optical coupler though an optical fiber. The optical coupler may be made from one of sapphire, fused silica, BK-7 glass, flint glass, germanium, and zinc selenide. The optical energy source may include a Nd:YAG laser, CTE:YAG laser, ErCr:YSGG laser, holmium laser, erbium laser, CO2 laser, diode laser, or dye laser. For example, suitable wavelength ranges include 1.7 to 2.2 xcexcm, 2.7 to 3.2 xcexcm, 10.6 xcexcm, and 420 to 510 nm.
In addition to animal and human tissue, the substrate treated by these methods or apparatus may also be a plastic, polymer, gel, a photosensitive coating, or other material that can be ablated and/or heated by optical energy. To provide laser-induced photochemical alteration of a substrate, UV optical energy may be used, e.g., from an excimer laser.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described below. All publications and patents mentioned herein are incorporated by reference. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
The embodiments of the invention include several advantages.
For example, the optical couplers permit a user to selectively control the optical penetration depth of laser energy delivered to a target. Moreover, the material and geometry of the coupler can prevent laser energy from exiting it when it is not contacting the target. The control over OPD permits precise photomedical alteration of tissue. Applications of the new device include superficial alteration of skin, wrinkle removal, corneal ablation laser angioplasty and other endoluminal ablation, dental applications, and laser lithotripsy.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.